Pipelines used to transport fluids are subject to different modes of failure such as leaking or bursting. Failure of a pipeline can begin at a location that is characterized by corrosion or other defects in the wall of the pipeline. If the corrosion or other defects are known, the pipeline can be preventatively maintained. For example, the pipeline can be repaired, replaced, or otherwise serviced, or the operating conditions of the pipeline can be adjusted to reflect changes in the pipeline. In some cases, preventative maintenance of the pipeline can prevent or reduce the likelihood of failure, extend the useful life of the pipeline, and reduce costs associated with repairs and downtime. Thus, an assessment regarding the condition of a pipeline can be important in determining whether maintenance is warranted, what type of maintenance should be performed, and the timing of the maintenance.
In order to assess the risk of pipeline failure due to a leak or burst, the current state of the pipeline is typically inferred from inspections. The results of periodic inspections can also be used to estimate the rate of deterioration of the pipeline condition, such as the corrosion rate of the pipe wall, and maintenance of the pipeline can be performed according to the results. Several methods have been developed to measure corrosion rates of the pipeline.
In-line inspection (ILI) methods use an instrument that moves through the pipeline and records locations of installations such as welds, anodes, flanges, and tie-ins, as well as features such as dents, gouges, material defects, and wall losses. The ILI instrument also provides information regarding whether the feature occurs on the internal or external side of the pipewall. For example, the ILI methods measure the location in the pipe of each feature, along with the length, width, and depth of each feature, and indicate the type of feature that is being measured. For example, an ILI method may conduct magnetic flux leakage (MFL) measurements or ultrasound (UT) measurements as the instrument travels through the pipeline.
In order to monitor the pipeline integrity and estimate a corrosion rate of the pipeline, the ILI measurements are repeated at subsequent times, and measured features are matched between a first ILI run and a second ILI run. The time-averaged corrosion rate is estimated by calculating changes in geometric characteristics of the matched features. For example, changes in the depth of a feature between successive ILI runs can indicate the likelihood of a leak in the pipeline. Similarly, changes in the depth and the width or length of a feature between successive ILI runs can indicate the likelihood of a pipeline burst.
If the likelihood of a leak or burst is determined to be greater than a threshold, the pipeline can be further monitored and/or maintenance can be performed to prevent a failure. Possible maintenance operations can include replacing all or part of a pipeline, applying a sleeve or patch-like layer to the outside of the pipeline, otherwise repairing the pipeline to correct defects, adjusting the operating conditions of the pipeline, or the like.